(a) Field of the Invention
The present invention relates to multi-layered thin films, a thin film transistor array panel including the same, and a method of manufacturing the panel.
(b) Description of Related Art
A thin film transistor (TFT) is generally used as a switching element to individually drive each pixel in a flat panel display such as a liquid crystal display or an organic light emitting display. A thin film transistor array panel including a plurality of TFTs has a plurality of pixel electrodes respectively connected to the TFTs, a plurality of gate lines for transmitting gate signals (scanning signals) to the TFTs, and a plurality of data lines for transmitting data signals to the TFTs.
The TFT includes a gate electrode connected to the gate line, a source electrode connected to the data line, a drain electrode connected to the pixel electrode, and a semiconductor layer overlapping the gate electrode via an insulating layer. The TFT controls the data signals applied to the pixel electrode according to the scanning signal of the gate line. The semiconductor layer of the TFT comprises amorphous silicon or crystalline silicon.
Because a polysilicon TFT has a relatively higher electron mobility than an amorphous silicon TFT, the polysilicon TFT made be applied to a high quality driving circuit. Also, the polysilicon TFT enables implementation of a chip-in-glass technique in which a display panel embeds its driving circuits therein.
The electrical characteristics of the TFT using polycrystalline silicon are influenced by the size and the uniformity of the silicon grain. The electric field effect mobility of the TFT increases according to increases in the size and the uniformity of grain.
Excimer laser annealing (ELA) and chamber annealing are typical methods for producing polycrystalline silicon. Recently, a sequential lateral solidification (SLS) process for deriving lateral growth of a silicon crystalline structure has been proposed.
The SLS technique for developing a large grain size provides good electric field effect mobility of the TFT compared with ELA. However, after the sequential lateral solidification, protrusions may form on the surface of the polysilicon layer along the grain boundaries, which increase the contact resistance between the polysilicon layer and the metal wire formed thereon.
To address this problem, many attempts have been made to provide methods of restraining the formation of protrusions. However, the resulting contact resistance between the polysilicon layer and the metal wire is still more than 10Ω and the distribution of threshold voltage of a TFT through the SLS technique is not improved compared with the TFT formed by the ELA technique. Finally, these protrusions decrease the electrical characteristics of the TFT such that the reliability of products incorporating the TFT may be deteriorated.
Gate lines and gate electrodes are typically made of a low resistivity metal such as aluminum. However, the tapered structure of the gate line does not vary and the contact resistance between the gate line and another metal layer may be large, such that electrical characteristics of the TFT are reduced.